Semiconductor device and method of forming the same

ABSTRACT

A semiconductor device may include, but is not limited to, a semiconductor substrate having a first gate groove; a first fin structure underneath the first gate groove; a first diffusion region in the semiconductor substrate, the first diffusion region covering an upper portion of a first side of the first gate groove; and a second diffusion region in the semiconductor substrate. The second diffusion region covers a second side of the first gate groove. The second diffusion region has a bottom which is deeper than a top of the first fin structure.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a semiconductor device and amethod of forming the same.

Priority is claimed on Japanese Patent Application No. 2011-102400,filed Apr. 28, 2011, the content of which is incorporated herein byreference.

2. Description of the Related Art

Recently, a size of a semiconductor device such as a dynamic randomaccess memory (DRAM) has decreased. Thereby, when a transistor isconfigured to have a short gate length, a short channel effect of thetransistor becomes remarkable, a sub-threshold current increases, and athreshold voltage (Vt) of the transistor decreases.

When an impurity concentration of a semiconductor substrate is increasedto suppress the threshold voltage (Vt) of the transistor fromdecreasing, a junction leak current may increase.

For this reason, when the DRAM is used as the semiconductor device and asize of a memory cell of the DRAM is decreased, a refresh characteristicis severely deteriorated.

As a structure to resolve the above problems, a so-called trench gatetype transistor (referred to as a “recess channel transistor”) in whicha gate electrode is buried in a groove formed on the side of a mainsurface of a semiconductor substrate is disclosed in Japanese Laid-OpenPatent Publications Nos. 2006-339476 and 2007-081095. By configuring thetransistor as the trench gate type transistor, an effective channellength (gate length) can be physically and sufficiently secured and aDRAM that has a fine cell in which a minimum processing dimension is 60nm or less can be realized.

Japanese Laid-Open Patent Publication No. 2007-081095 discloses a DRAMthat includes two grooves formed in a semiconductor substrate to beadjacent to each other, gate electrodes formed in the grooves through agate insulating film, a first impurity diffusion region formed in a mainsurface of the semiconductor substrate positioned between the two gateelectrodes as an impurity diffusion region common to the two gateelectrodes, and a second impurity diffusion region formed in the mainsurface of the semiconductor substrate positioned at an elementisolation region side of the two gate electrodes.

In the DRAM that has the trench gate type transistor described inJapanese Laid-Open Patent Publications Nos. 2006-339476 and 2007-081095,a channel region of the transistor is formed on three surfaces of bothsides and a bottom surface of a trench.

The inventors have found that an on-state current of the transistorcannot be sufficiently secured and a normal operation of the DRAMbecomes difficult when the size of the transistor having theabove-described configuration is further decreased. This phenomenon isgenerated because the channel region of the transistor is formed on thethree surfaces forming the trench and channel resistance increases, asdescribed above.

If an arrangement pitch of the trench gate is narrowed, when a certaintransistor is operated, an operation state of the transistor interfereswith another transistor adjacent to the transistor and the transistorcannot be operated independently.

This phenomenon is generated because the channel region is formedbetween the adjacent trench gates.

In the trench gate type transistor, because the gate electrode is formedto protrude to an upper side of a surface of the semiconductorsubstrate, it becomes very difficult to form a bit line or a capacitorto be formed in the following process due to the protruding gateelectrode and it becomes difficult to manufacture the DRAM.

Accordingly, there is a demand to provide a semiconductor device and amanufacturing method thereof that can sufficiently secure an on-statecurrent of a transistor, prevent operation interference of adjacenttransistors, and resolve manufacturing difficulty in the DRAM includingthe transistor using the trench.

SUMMARY

In one embodiment, a semiconductor device may include, but is notlimited to, a semiconductor substrate having a first gate groove; afirst fin structure underneath the first gate groove; a first diffusionregion in the semiconductor substrate, the first diffusion regioncovering an upper portion of a first side of the first gate groove; anda second diffusion region in the semiconductor substrate. The seconddiffusion region covers a second side of the first gate groove. Thesecond diffusion region has a bottom which is deeper than a top of thefirst fin structure.

In another embodiment, a semiconductor device may include, but is notlimited to, a semiconductor substrate having a first gate groove; afirst fin structure underneath the first gate groove; a first diffusionregion in the semiconductor substrate, the first diffusion regioncovering an upper portion of a first side of the first gate groove; asecond diffusion region in the semiconductor substrate, the seconddiffusion region covering a second side of the first gate groove; and achannel region extending. The channel region extends between the firstand second diffusion regions through the surface of the fin structureand along the first side of the first gate groove, without the channelregion extending along the second side of the first gate groove.

In still another embodiment, a semiconductor device may include, but isnot limited to, a semiconductor substrate having a first gate groove; afirst fin structure underneath the first gate groove; a first diffusionregion in the semiconductor substrate, the first diffusion regioncovering an upper portion of a first side of the first gate groove; anda second diffusion region in the semiconductor substrate, the seconddiffusion region covering a second side of the first gate groove. Thefirst gate groove has a bottom that has a depth from a surface of thesemiconductor substrate in the range from 150 nm to 200 nm, and thefirst fin structure has a height in the range from 10 nm to 40 nm.

BRIEF DESCRIPTION OF THE DRAWINGS

The above features and advantages of the present invention will be moreapparent from the following description of certain preferred embodimentstaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a fragmentary schematic plan view of a memory cell array of asemiconductor device in accordance with one or more embodiments of theinvention;

FIG. 2A is a fragmentary cross sectional elevation view of the memorycell array, taken along an A-A line of FIG. 1;

FIG. 2B is a fragmentary cross sectional elevation view of the memorycell array, taken along a B-B line of FIG. 1;

FIG. 2C is a fragmentary perspective view of the semiconductor deviceincluding a fin structure of FIGS. 1, 2A and 2B;

FIG. 3A is a fragmentary plan view of a step involved in a method offorming a memory cell array of the semiconductor device of FIGS. 1, 2A,2B, and 2C;

FIG. 3B is a fragmentary cross sectional elevation view, taken along anA-A line of FIG. 3A, of the step involved in the method of forming thememory cell array of the semiconductor device of FIGS. 1, 2A, 2B, and2C;

FIG. 3C is a fragmentary cross sectional elevation view, taken along aB-B line of FIG. 3A, of the step involved in the method of forming thememory cell array of the semiconductor device of FIGS. 1, 2A, 2B, and2C;

FIG. 3D is a fragmentary cross sectional elevation view, taken along aC-C line of FIG. 3A, of the step involved in the method of forming thememory cell array of the semiconductor device of FIGS. 1, 2A, 2B, and2C;

FIG. 4A is a fragmentary plan view of a step, subsequent to the step ofFIGS. 3A, 3B, 3C and 3D, involved in a method of forming a memory cellarray of the semiconductor device of FIGS. 1, 2A, 2B, and 2C;

FIG. 4B is a fragmentary cross sectional elevation view, taken along anA-A line of FIG. 4A, of the step, subsequent to the step of FIGS. 3A,3B, 3C and 3D, involved in the method of forming the memory cell arrayof the semiconductor device of FIGS. 1, 2A, 2B, and 2C;

FIG. 4C is a fragmentary cross sectional elevation view, taken along aB-B line of FIG. 4A, of the step, subsequent to the step of FIGS. 3A,3B, 3C and 3D, involved in the method of forming the memory cell arrayof the semiconductor device of FIGS. 1, 2A, 2B, and 2C;

FIG. 4D is a fragmentary cross sectional elevation view, taken along aC-C line of FIG. 4A, of the step, subsequent to the step of FIGS. 3A,3B, 3C and 3D, involved in the method of forming the memory cell arrayof the semiconductor device of FIGS. 1, 2A, 2B, and 2C;

FIG. 5A is a fragmentary plan view of a step, subsequent to the step ofFIGS. 4A, 4B, 4C and 4D, involved in a method of forming a memory cellarray of the semiconductor device of FIGS. 1, 2A, 2B, and 2C;

FIG. 5B is a fragmentary cross sectional elevation view, taken along anA-A line of FIG. 5A, of the step, subsequent to the step of FIGS. 4A,4B, 4C and 4D, involved in the method of forming the memory cell arrayof the semiconductor device of FIGS. 1, 2A, 2B, and 2C;

FIG. 5C is a fragmentary cross sectional elevation view, taken along aB-B line of FIG. 5A, of the step, subsequent to the step of FIGS. 4A,4B, 4C and 4D, involved in the method of forming the memory cell arrayof the semiconductor device of FIGS. 1, 2A, 2B, and 2C;

FIG. 5D is a fragmentary cross sectional elevation view, taken along aC-C line of FIG. 5A, of the step, subsequent to the step of FIGS. 4A,4B, 4C and 4D, involved in the method of forming the memory cell arrayof the semiconductor device of FIGS. 1, 2A, 2B, and 2C;

FIG. 6A is a fragmentary plan view of a step, subsequent to the step ofFIGS. 5A, 5B, 5C and 5D, involved in a method of forming a memory cellarray of the semiconductor device of FIGS. 1, 2A, 2B, and 2C;

FIG. 6B is a fragmentary cross sectional elevation view, taken along anA-A line of FIG. 6A, of the step, subsequent to the step of FIGS. 5A,5B, 5C and 5D, involved in the method of forming the memory cell arrayof the semiconductor device of FIGS. 1, 2A, 2B, and 2C;

FIG. 6C is a fragmentary cross sectional elevation view, taken along aB-B line of FIG. 6A, of the step, subsequent to the step of FIGS. 5A,5B, 5C and 5D, involved in the method of forming the memory cell arrayof the semiconductor device of FIGS. 1, 2A, 2B, and 2C;

FIG. 6D is a fragmentary cross sectional elevation view, taken along aC-C line of FIG. 6A, of the step, subsequent to the step of FIGS. 5A,5B, 5C and 5D, involved in the method of forming the memory cell arrayof the semiconductor device of FIGS. 1, 2A, 2B, and 2C;

FIG. 7A is a fragmentary plan view of a step, subsequent to the step ofFIGS. 6A, 6B, 6C and 6D, involved in a method of forming a memory cellarray of the semiconductor device of FIGS. 1, 2A, 2B, and 2C;

FIG. 7B is a fragmentary cross sectional elevation view, taken along anA-A line of FIG. 7A, of the step, subsequent to the step of FIGS. 6A,6B, 6C and 6D, involved in the method of forming the memory cell arrayof the semiconductor device of FIGS. 1, 2A, 2B, and 2C;

FIG. 7C is a fragmentary cross sectional elevation view, taken along aB-B line of FIG. 7A, of the step, subsequent to the step of FIGS. 6A,6B, 6C and 6D, involved in the method of forming the memory cell arrayof the semiconductor device of FIGS. 1, 2A, 2B, and 2C;

FIG. 7D is a fragmentary cross sectional elevation view, taken along aC-C line of FIG. 7A, of the step, subsequent to the step of FIGS. 6A,6B, 6C and 6D, involved in the method of forming the memory cell arrayof the semiconductor device of FIGS. 1, 2A, 2B, and 2C;

FIG. 8A is a fragmentary plan view of a step, subsequent to the step ofFIGS. 7A, 7B, 7C and 7D, involved in a method of forming a memory cellarray of the semiconductor device of FIGS. 1, 2A, 2B, and 2C;

FIG. 8B is a fragmentary cross sectional elevation view, taken along anA-A line of FIG. 8A, of the step, subsequent to the step of FIGS. 7A,7B, 7C and 7D, involved in the method of forming the memory cell arrayof the semiconductor device of FIGS. 1, 2A, 2B, and 2C;

FIG. 8C is a fragmentary cross sectional elevation view, taken along aB-B line of FIG. 8A, of the step, subsequent to the step of FIGS. 7A,7B, 7C and 7D, involved in the method of forming the memory cell arrayof the semiconductor device of FIGS. 1, 2A, 2B, and 2C;

FIG. 8D is a fragmentary cross sectional elevation view, taken along aC-C line of FIG. 8A, of the step, subsequent to the step of FIGS. 7A,7B, 7C and 7D, involved in the method of forming the memory cell arrayof the semiconductor device of FIGS. 1, 2A, 2B, and 2C;

FIG. 9A is a fragmentary plan view of a step, subsequent to the step ofFIGS. 8A, 8B, 8C and 8D, involved in a method of forming a memory cellarray of the semiconductor device of FIGS. 1, 2A, 2B, and 2C;

FIG. 9B is a fragmentary cross sectional elevation view, taken along anA-A line of FIG. 9A, of the step, subsequent to the step of FIGS. 8A,8B, 8C and 8D, involved in the method of forming the memory cell arrayof the semiconductor device of FIGS. 1, 2A, 2B, and 2C;

FIG. 9C is a fragmentary cross sectional elevation view, taken along aB-B line of FIG. 9A, of the step, subsequent to the step of FIGS. 8A,8B, 8C and 8D, involved in the method of forming the memory cell arrayof the semiconductor device of FIGS. 1, 2A, 2B, and 2C;

FIG. 9D is a fragmentary cross sectional elevation view, taken along aC-C line of FIG. 9A, of the step, subsequent to the step of FIGS. 8A,8B, 8C and 8D, involved in the method of forming the memory cell arrayof the semiconductor device of FIGS. 1, 2A, 2B, and 2C;

FIG. 10A is a fragmentary plan view of a step, subsequent to the step ofFIGS. 9A, 9B, 9C and 9D, involved in a method of forming a memory cellarray of the semiconductor device of FIGS. 1, 2A, 2B, and 2C;

FIG. 10B is a fragmentary cross sectional elevation view, taken along anA-A line of FIG. 10A, of the step, subsequent to the step of FIGS. 9A,9B, 9C and 9D, involved in the method of forming the memory cell arrayof the semiconductor device of FIGS. 1, 2A, 2B, and 2C;

FIG. 10C is a fragmentary cross sectional elevation view, taken along aB-B line of FIG. 10A, of the step, subsequent to the step of FIGS. 9A,9B, 9C and 9D, involved in the method of forming the memory cell arrayof the semiconductor device of FIGS. 1, 2A, 2B, and 2C;

FIG. 11A is a fragmentary plan view of a step, subsequent to the step ofFIGS. 10A, 10B, and 10C, involved in a method of forming a memory cellarray of the semiconductor device of FIGS. 1, 2A, 2B, and 2C;

FIG. 11B is a fragmentary cross sectional elevation view, taken along anA-A line of FIG. 11A, of the step, subsequent to the step of FIGS. 10A,10B, and 10C, involved in the method of forming the memory cell array ofthe semiconductor device of FIGS. 1, 2A, 2B, and 2C;

FIG. 11C is a fragmentary cross sectional elevation view, taken along aB-B line of FIG. 11A, of the step, subsequent to the step of FIGS. 10A,10B, and 10C, involved in the method of forming the memory cell array ofthe semiconductor device of FIGS. 1, 2A, 2B, and 2C;

FIG. 12A is a fragmentary plan view of a step, subsequent to the step ofFIGS. 11A, 11B, and 11C, involved in a method of forming a memory cellarray of the semiconductor device of FIGS. 1, 2A, 2B, and 2C;

FIG. 12B is a fragmentary cross sectional elevation view, taken along anA-A line of FIG. 12A, of the step, subsequent to the step of FIGS. 11A,11B, and 11C, involved in the method of forming the memory cell array ofthe semiconductor device of FIGS. 1, 2A, 2B, and 2C;

FIG. 12C is a fragmentary cross sectional elevation view, taken along aB-B line of FIG. 12A, of the step, subsequent to the step of FIGS. 11A,11B, and 11C, involved in the method of forming the memory cell array ofthe semiconductor device of FIGS. 1, 2A, 2B, and 2C;

FIG. 13A is a fragmentary plan view of a step, subsequent to the step ofFIGS. 12A, 12B, and 12C, involved in a method of forming a memory cellarray of the semiconductor device of FIGS. 1, 2A, 2B, and 2C;

FIG. 13B is a fragmentary cross sectional elevation view, taken along anA-A line of FIG. 13A, of the step, subsequent to the step of FIGS. 12A,12B, and 12C, involved in the method of forming the memory cell array ofthe semiconductor device of FIGS. 1, 2A, 2B, and 2C;

FIG. 13C is a fragmentary cross sectional elevation view, taken along aB-B line of FIG. 13A, of the step, subsequent to the step of FIGS. 12A,12B, and 12C, involved in the method of forming the memory cell array ofthe semiconductor device of FIGS. 1, 2A, 2B, and 2C;

FIG. 14A is a fragmentary plan view of a step, subsequent to the step ofFIGS. 13A, 13B, and 13C, involved in a method of forming a memory cellarray of the semiconductor device of FIGS. 1, 2A, 2B, and 2C;

FIG. 14B is a fragmentary cross sectional elevation view, taken along anA-A line of FIG. 14A, of the step, subsequent to the step of FIGS. 13A,13B, and 13C, involved in the method of forming the memory cell array ofthe semiconductor device of FIGS. 1, 2A, 2B, and 2C;

FIG. 15A is a fragmentary plan view of a step, subsequent to the step ofFIGS. 14A, and 14B, involved in a method of forming a memory cell arrayof the semiconductor device of FIGS. 1, 2A, 2B, and 2C;

FIG. 15B is a fragmentary cross sectional elevation view, taken along anA-A line of FIG. 15A, of the step, subsequent to the step of FIGS. 14A,and 14B, involved in the method of forming the memory cell array of thesemiconductor device of FIGS. 1, 2A, 2B, and 2C;

FIG. 16A is a fragmentary plan view of a step, subsequent to the step ofFIGS. 15A, and 15B, involved in a method of forming a memory cell arrayof the semiconductor device of FIGS. 1, 2A, 2B, and 2C;

FIG. 16B is a fragmentary cross sectional elevation view, taken along anA-A line of FIG. 16A, of the step, subsequent to the step of FIGS. 15A,and 15B, involved in the method of forming the memory cell array of thesemiconductor device of FIGS. 1, 2A, 2B, and 2C;

FIG. 17 is a fragmentary schematic plan view of another memory cellarray of a semiconductor device in accordance with other embodiments ofthe invention;

FIG. 18 is a diagram illustrating variation of failure rate over heightof fin structure;

FIG. 19 is a diagram illustrating variation of failure rate over depthof second impurity diffusion region;

FIG. 20 is a diagram illustrating variation of impurity concentrationover depth from surface of semiconductor substrate;

FIG. 21 is a fragmentary schematic plan view of a memory cell array of asemiconductor device in the related art; and

FIG. 22 is a fragmentary cross sectional elevation view of a memory cellarray of the semiconductor device in the related art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Before describing the present invention, the related art will beexplained in detail with reference to FIGS. 21, and 22, in order tofacilitate the understanding of the present invention.

The inventors have discovered the following new fact. If a size of amemory cell of a dynamic random access memory (DRAM) decreases, aninterval between two adjacent cells that are provided in one activeregion decreases. As a result, when data “0” is stored in one cell anddata “1” is stored in the other cell and access is continuouslyperformed with respect to the cell storing the data “0,” a disturbancefailure between adjacent cells (hereinafter, simply referred to as a“disturbance failure”) in which the data “1” stored in the cell isdestroyed is generated. The disturbance failure lowers reliability of asemiconductor device.

FIG. 21 is a plan view showing an example of a layout of a DRAMaccording to the related art and FIG. 22 is a cross-sectional view ofthe DRAM shown in FIG. 21 in a Z-Z direction.

Next, what the inventors discovered with respect to the disturbancefailure described above will be described with reference to FIGS. 21 and22.

Referring to FIG. 21, a plurality of active regions 302 are regularlyarranged on a surface of a semiconductor substrate 301. Each activeregion 302 is surrounded by an element isolation region 303 that buriesa groove formed in the surface of the semiconductor substrate 301 withan insulating film. In a Y direction that crosses the active region 302,a plurality of word lines WL that extend in the Y direction arearranged.

Referring to FIG. 22, word lines WL1 and WL2 are formed to be buriedthrough a gate insulating film 305 in grooves provided over theplurality of active regions 302 and the element isolation region 303 inthe surface of the semiconductor substrate 301.

On top surfaces of the word lines WL1 and WL2, cap insulating films 306are formed to be buried in the grooves. In one active region 302, twoword lines, that is, the word lines WL1 and WL2, are provided to crossthe active region 302.

The two word lines WL1 and WL2 form gate electrodes of two transistorsTr1 and Tr2 that correspond to the word lines. The transistor Tr1includes the gate electrode formed of the word line WL1, a draindiffusion layer 307, and a source diffusion layer 308.

The transistor Tr2 includes the gate electrode formed of the word lineWL2, a drain diffusion layer 312, and the source diffusion layer 308.The source diffusion layer 308 is common to the transistors Tr1 and Tr2and is connected to a bit line BL in a bit line contact 311.

Meanwhile, the drain diffusion layers 307 and 312 are connected to lowerelectrodes 313 and 314 (storage nodes) through a capacitor contact plug310 formed in an interlayer insulating film 309.

The lower electrodes 313 and 314 form capacitive elements 316 and 317with capacitor insulating films and upper electrodes (not shown in thedrawings), respectively. The surface of the semiconductor substrate 301that corresponds to bottom surfaces of the grooves in which the wordlines WL1 and WL2 are buried and two facing sides becomes channels ofthe transistors Tr1 and Tr2.

For example, if a state of the word line WL1 is set to an on state, achannel of the transistor Tr1 is formed, and potential of a low (L)level is applied to a bit line 319, a state of the lower electrode 313becomes an “L” state. Then, if the state of the word line WL1 is set toan off state, information of L (data “0”) is stored in the lowerelectrode 313.

For example, if a state of the word line WL2 is set to an on state, achannel of the transistor Tr2 is formed, and potential of a high (H)level is applied to the bit line 319, a state of the lower electrode 314becomes an “H” state. Then, if the state of the word line WL2 is set toan off state, information of H (data “1”) is stored in the lowerelectrode 314.

On the basis of the operation state, “L” is stored in the lowerelectrode 313 and “H” is stored in the lower electrode 314. In thisstate, on/off of the word line WL1 that corresponds to the L-side lowerelectrode 313 is repeated (which corresponds to a cell operation ofanother active region using the same word line WL1).

As a result, electrons “e⁻” that are induced in the channel of thetransistor Tr1 may reach the adjacent drain diffusion layer 312, destroythe “H” information stored in the lower electrode 314, and change thestate of the lower electrode 314 to the “L” state.

That is, a failure of a mode in which the data “1” changes the data “0”is generated. The failure depends on the number of times of on/off ofthe word line WL1. For example, if the number of times of on/off is10,000 times, one of the plurality of cells is destroyed and if thenumber of times of on/off is 100,000 times, ten cells are destroyed.

Each of the adjacent cells originally needs to hold informationindependently. However, if the disturbance failure in which an operationstate of one adjacent cell changes a storage state of another adjacentcell is generated, a normal operation of the semiconductor device (DRAM)is disturbed and reliability is lowered.

The disturbance failure is not generated when a cell size is large, thatis, when an interval L between the word lines WL1 and WL2 defined with aminimum processing dimension F is 70 nm as shown in FIG. 21.

However, if the memory cell is reduced and the interval between the wordlines WL1 and WL2 is less than 50 nm, the disturbance failure becomesremarkable. If the interval further decreases, the disturbance failurebecomes further remarkable.

Embodiments of the invention will be now described herein with referenceto illustrative embodiments. Those skilled in the art will recognizethat many alternative embodiments can be accomplished using the teachingof the embodiments of the present invention and that the invention isnot limited to the embodiments illustrated for explanatory purpose.

In one embodiment, a semiconductor device may include, but is notlimited to, a semiconductor substrate having a first gate groove; afirst fin structure underneath the first gate groove; a first diffusionregion in the semiconductor substrate, the first diffusion regioncovering an upper portion of a first side of the first gate groove; anda second diffusion region in the semiconductor substrate. The seconddiffusion region covers a second side of the first gate groove. Thesecond diffusion region has a bottom which is deeper than a top of thefirst fin structure.

In some cases, the bottom of the second diffusion region is shallowerthan a bottom of the first fin structure.

In some cases, the first gate groove has a bottom that has a depth froma surface of the semiconductor substrate in the range from 150 nm to 200nm, and the first fin structure has a height in the range from 10 nm to40 nm.

In some cases, the semiconductor device may further include, but is notlimited to, a first gate insulating film that covers the first gategroove and a surface of the first fin structure; and a first gateelectrode on the first gate insulating film in a lower portion of thefirst gate groove. The first gate electrode extends over the first finstructure.

In some cases, the semiconductor substrate has a second gate groovehaving a first groove that is covered by the second diffusion region.

In some cases, the semiconductor device may further include, but is notlimited to, a second fin structure underneath the second gate groove;and a third diffusion region in the semiconductor substrate. The thirddiffusion region covers an upper portion of a first side of the secondgate groove. The second diffusion region has a bottom which is deeperthan a top of the second fin structure and shallower than a bottom ofthe second fin structure.

In some cases, the second gate groove has a bottom that has a depth froma surface of the semiconductor substrate in the range from 150 nm to 200nm, and the second fin structure has a height in the range from 10 nm to40 nm.

In some cases, the semiconductor device may further include, but is notlimited to, a second gate insulating film that covers the second gategroove and a surface of the second fin structure; and a second gateelectrode on the second gate insulating film in a lower portion of thesecond gate groove. The second gate electrode extends over the secondfin structure.

In some cases, the first diffusion region has a bottom that which isshallower by a range of 5 nm to 10 nm than a top surface of the gateelectrode.

In some cases, the first fin structure has a top ridge and first andsecond side surfaces opposing to each other. The top ridge extendsbetween the first and second sides of the first gate groove. The firstand second side surfaces extend in parallel to a first direction inwhich the top ridge extends.

In some cases, the semiconductor device may further include, but is notlimited to, a plurality of first isolation regions in the semiconductordevice. The plurality of first isolation regions defines active regions.The plurality of first isolation regions extend in the first direction.The gate groove extends in a second direction and across the activeregion and the first isolation region.

In some cases, the semiconductor device may further include, but is notlimited to, a plurality of second isolation regions extending in asecond direction and in the semiconductor device. The plurality ofsecond isolation regions defines device regions in each of the activeregions.

In some cases, the semiconductor device may further include, but is notlimited to, a bit line electrically coupled to the second diffusionregion. The bit line extends across the gate groove.

In some cases, the semiconductor device may further include, but is notlimited to, a capacitor electrically coupled to the first diffusionregion.

In some cases, the semiconductor device may further include, but is notlimited to, a channel region extending between the first and seconddiffusion regions through the surface of the fin structure and along thefirst side of the first gate groove, without the channel regionextending along the second side of the first gate groove.

In some cases, the semiconductor device may further include, but is notlimited to, a channel region extending from a bottom of the firstdiffusion region and along the first side of the first gate groove. Thechannel region further extends along the bottom of the first gategroove. The channel region further extends from the second diffusionregion and along the second side of the first gate groove.

In some cases, the first gate insulating film has an equivalent oxidethickness in the range of 4 nm to 6 nm, and the gate electrode has awork function in the range from 4.6 eV to 4.8 eV, and the first gateelectrode has a threshold voltage in the range from 0.8 V to 1.0 V.

In another embodiment, a semiconductor device may include, but is notlimited to, a semiconductor substrate having a first gate groove; afirst fin structure underneath the first gate groove; a first diffusionregion in the semiconductor substrate, the first diffusion regioncovering an upper portion of a first side of the first gate groove; asecond diffusion region in the semiconductor substrate, the seconddiffusion region covering a second side of the first gate groove; and achannel region extending. The channel region extends between the firstand second diffusion regions through the surface of the fin structureand along the first side of the first gate groove, without the channelregion extending along the second side of the first gate groove.

In some cases, the first gate groove has a bottom that has a depth froma surface of the semiconductor substrate in the range from 150 nm to 200nm, and the first fin structure has a height in the range from 10 nm to40 nm.

In still another embodiment, a semiconductor device may include, but isnot limited to, a semiconductor substrate having a first gate groove; afirst fin structure underneath the first gate groove; a first diffusionregion in the semiconductor substrate, the first diffusion regioncovering an upper portion of a first side of the first gate groove; anda second diffusion region in the semiconductor substrate, the seconddiffusion region covering a second side of the first gate groove. Thefirst gate groove has a bottom that has a depth from a surface of thesemiconductor substrate in the range from 150 nm to 200 nm, and thefirst fin structure has a height in the range from 10 nm to 40 nm.

In the semiconductor device according to the present invention, a firstimpurity diffusion region that covers an upper portion of a gateinsulating film arranged on a first side and a second impurity diffusionregion that covers the gate insulating film arranged on at least asecond side are provided in the semiconductor substrate and a finportion that is formed such that a part of an active region protrudesfrom a bottom portion of a gate electrode groove is provided. As aresult, because a channel region is formed on two surfaces of the bottomportion of the gate electrode groove and a lower portion of the firstside and the fin portion, the channel resistance can be decreased ascompared with the semiconductor device according to the related art inwhich the channel region is formed on three surfaces of the bottomsurface and the facing sides of the gate electrode groove. Thereby, theon-state current of the transistor can be sufficiently secured.

The gate electrode groove is provided in the second side of the gateelectrode groove and another transistor is arranged on the gateelectrode groove to be adjacent thereto. As a result, the channel regionis not formed between the gate electrode grooves. Thereby, when thearrangement pitch of the gate electrode grooves is narrowed, even when acertain transistor is operated, the operation state thereof does notinterfere with another transistor adjacent to the certain transistor.Therefore, each transistor can be operated independently.

The gate electrode that is arranged to bury a lower portion of the gateelectrode groove and step over the fin portion through the gateinsulating film and the buried insulating film that is arranged to burythe gate electrode groove and covers the top surface of the gateelectrode are provided and the gate electrode can be prevented fromprotruding to the upper side of the surface of the semiconductorsubstrate. Thereby, when the DRAM is used as the semiconductor device,the bit line or the capacitor that is formed in the following processcan be easily formed. Therefore, the semiconductor device can be easilymanufactured.

EMBODIMENTS Semiconductor Device

FIG. 1 is a schematic plan view of a memory cell array that is providedin the semiconductor device according to the embodiment of the presentinvention. FIG. 2A is a cross-sectional view of the memory cell arrayshown in FIG. 1 in an A-A direction. FIG. 2B is a cross-sectional viewof the memory cell array shown in FIG. 1 in a B-B direction. FIG. 2C isa perspective view showing a cross-sectional structure of a fin portionthat is provided in a gate electrode groove in the semiconductor deviceaccording to this embodiment.

In FIGS. 1, 2A, and 2B, a dynamic random access memory (DRAM) is shownas an example of a semiconductor device 10 according to the embodimentof the present invention. FIG. 1 shows an example of a layout of amemory cell array of the DRAM.

In FIG. 1, an X direction shows an extension direction of a bit line 34and a Y direction shows an extension direction (second direction) of agate electrode 22 and a second element isolation region 17 crossing an Xdirection.

In FIG. 1, only a semiconductor substrate 13, a first element isolationregion 14, an active region 16, the second element isolation region 17,a gate electrode groove 18, the gate electrode 22, the bit line 34, acapacitor contact plug 42, a capacitor contact pad 44, and a pluralityof element formation regions R among components of a memory cell array11 are shown and the other components of the memory cell array 11 arenot shown, to simplify the description.

FIG. 2A schematically shows the bit line 34 that extends in the Xdirection shown in FIG. 1. In FIGS. 2A to 2C, the same components asthose of the semiconductor device 10 shown in FIG. 1 are denoted by thesame reference numerals.

The semiconductor device 10 according to the embodiment of the presentinvention has a memory cell region that is provided with the memory cellarray 11 shown in FIGS. 1, 2A, and 2B and a peripheral circuit region(formation region of a peripheral circuit) (not shown in the drawings)that is arranged around a memory cell region.

As shown in FIGS. 1, 2A, and 2B, the memory cell array 11 that isprovided in the semiconductor device 10 includes the semiconductorsubstrate 13, the first element isolation region 14, the active region16 having the plurality of element formation regions R, the secondelement isolation region 17, the gate electrode groove 18, a fin portion15 that is formed such that a part of the active region 16 protrudesfrom a bottom portion 18 c of the gate electrode groove 18, first andsecond transistors 19-1 and 19-2, a gate insulating film 21, the gateelectrode 22 that is a buried type gate electrode, a buried insulatingfilm 24, a mask insulating film 26, a first impurity diffusion region28, a second impurity diffusion region 29, an opening 32, a bit linecontact plug 33, a bit line 34, a cap insulating film 36, a sidewallfilm 37, an interlayer insulating film 38, a contact hole 41, acapacitor contact plug 42, a capacitor contact pad 44, a silicon nitridefilm 46, and a capacitor 48.

As shown in FIGS. 1, 2A, and 2B, the semiconductor substrate 13 is asubstrate that is formed in a plate shape.

As the semiconductor substrate 13, a p-type single crystalline siliconsubstrate may be used. In this case, a p-type impurity concentration ofthe semiconductor substrate 13 may be set to 1E16 atoms/cm².

As shown in FIG. 1, the first element isolation region 14 has a firstelement isolation groove 51 and a first element isolation insulatingfilm 52. The first element isolation grooves 51 are formed in thesemiconductor substrate 13 to extend in a direction (first direction)inclined with respect to the X direction shown in FIG. 1 by apredetermined angle. The first element isolation grooves 51 are formedat a predetermined interval with respect to the Y direction shown inFIG. 1. The depth of the first element isolation groove 51 may be set to250 nm.

The first element isolation insulating films 52 are arranged to bury thefirst element isolation grooves 51. Although not shown in the drawings,a top surface of the first element isolation insulating film 52 is flushwith a main surface 13 a of the semiconductor substrate 13. As the firstelement isolation insulating film 52, a silicon oxide film (SiO₂ film)may be used.

The first element isolation region 14 that has the above-describedconfiguration partitions the active region 16 that extends in a stripeshape with respect to the second direction.

As shown in FIGS. 1, 2A, and 2B, the second element isolation region 17has a second element isolation groove 54 and a second element isolationinsulating film 55. The second element isolation groove 54 is formed inthe semiconductor substrate 13 to extend in the Y direction (seconddirection) shown in FIG. 1. Thereby, the second element isolation groove54 cuts a part of the first element isolation region 14. The secondelement isolation groove 54 is formed to sandwich the two gateelectrodes 22 arranged to be adjacent to the second element isolationgroove.

Each of the gate electrodes 22 forms a word line of the memory cell.That is, the memory cell according to this embodiment is configured suchthat one second element isolation region 17 and the two gate electrodes22 (word lines) extending in the Y direction form a pair and arerepetitively arranged in the X direction.

The depth of the second element isolation groove 54 may be set to 250nm.

The second element isolation insulating film 55 is arranged to bury thesecond element isolation groove 54 and an opening 26A formed in the maskinsulating film 26. A top surface 55 a of the second element isolationinsulating film 55 is flush with a top surface 26 a of the maskinsulating film 26. As the second element isolation insulating film 55,a silicon oxide film (SiO₂ film) may be used.

The second element isolation region 17 that has the above-describedconfiguration partitions the plurality of element formation regions Rwith respect to the second direction.

As such, the first element isolation region 14 that is formed by buryingthe first element isolation insulating film 52 in the first elementisolation groove 51 formed in the semiconductor substrate 13 and thesecond element isolation region 17 that is formed by burying the secondelement isolation insulating film 55 in the second element isolationgroove 54 in the semiconductor substrate 13 are provided and the activeregion 16 is partitioned into the plurality of element formation regionsR. As a result, as compared with the case in which a dummy gateelectrode (not shown in the drawings) to which negative potential isapplied is provided in the second element isolation groove 54 throughthe gate insulating film 21 and the plurality of element formationregions R are partitioned, the potential of the dummy gate electrodedoes not exert a bad influence upon the first and second transistors19-1 and 19-2. Therefore, the first and second transistors 19-1 and 19-2may be easily turned on and a retention characteristic of the data ofthe memory cell array 11 may be improved.

As shown in FIGS. 1, 2A, and 2B, the two (pair of) gate electrodegrooves 18 are provided in the semiconductor substrate 13 positionedbetween the two second element isolation regions 17 to extend in the Ydirection. The gate electrode groove 18 is partitioned by an innersurface including the first and second sides 18 a and 18 b facing eachother and the bottom portion 18 c. The pair of gate electrode grooves 18are arranged such that the second sides 18 b face each other.

As shown in FIGS. 2B and 2C, the gate electrode groove 18 is configuredsuch that the depth of the bottom portion 18 c thereof is less than thedepths of the first and second element isolation grooves 51 and 54(depths of the first and second element isolation regions 14 and 17).When the depths of the first and second element isolation grooves 51 and54 are 250 nm, the depth of the gate electrode groove 18 is preferablyset to 150 to 200 nm.

As shown in FIGS. 1 and 2C, the gate electrode groove 18 extends totransverse the first element isolation region 14 and the active region16. That is, the gate electrode groove 18 is configured such that thefirst groove portion 18A formed in the active region 16 is continuous tothe second groove portion 18B formed in the first element isolationregion 14.

As shown in FIGS. 2B and 2C, the bottom portion of the second grooveportion 18B of the gate electrode groove 18 that is formed in the firstelement isolation region 14 becomes the bottom portion 18 c of the gateelectrode groove 18.

As shown in FIGS. 2A and 2C, the bottom portion of the first grooveportion 18A of the gate electrode groove 18 that is formed in the activeregion 16 is configured such that the depth of an end facing the secondgroove portion 18B is equal to the depth of the bottom portion of thesecond groove portion. Meanwhile, in a center portion of the firstgroove portion 18A, the fin portion 15 is formed such that a part of theactive region 16 protrudes from the bottom portion.

As shown in FIGS. 2A to 2C, the fin portion 15 has an upper portion 15 aand a pair of facing sides 15 b and 15 c.

The upper portion 15 a extends in an extension direction (firstdirection) of the active region 16. Both ends of the upper portion 15 ain the extension direction are provided over the first side 18 a and thesecond side 18 b forming the gate electrode groove 18 in the firstgroove portion 18A.

The pair of sides 15 b and 15 c are arranged to be parallel to theextension direction (first direction) of the active region 16.

As a shape of the fin portion 15, a corner may have an acute angle andmay be round (may not have the acute angle), as shown in FIG. 2C.

In this embodiment, the height of the fin portion 15 means the heightfrom a lowest portion of the bottom portion 18 c of the gate electrodegroove 18 to a portion contacting the upper portion 15 a extending in avertical direction, as shown by H in FIG. 2C.

The height H of the fin portion 15 is preferably in a range of 10 to 40nm when the depth of the gate electrode groove 18 is 150 to 220 nm. Inother words, the upper portion 15 a of the fin portion 15 is preferablypositioned at the depth of 100 nm or more from the surface of thesemiconductor substrate 13.

When the height H of the fin portion 15 is less than 10 nm, this is notpreferable because a subthreshold factor (S factor) increases and an OFFleak current increases. This is not preferable because a current drivingcapability is lowered and a writing characteristic is deteriorated.Meanwhile, if the height H of the fin portion 15 is more than 40 nm,this is not preferable because the disturbance failure is notsufficiently suppressed.

Meanwhile, if the height H of the fin portion 15 is within this range,the OFF leak current may be suppressed from increasing and the writingcharacteristic may be improved, while the disturbance failure issufficiently suppressed. That is, all of the characteristics that are ina trade-off relation with the height of the fin portion may be satisfied(refer to FIG. 18).

Referring to FIGS. 2A to 2C, each of the first and second transistors19-1 and 19-2 is a trench gate type transistor and has the gateinsulating film 21, the gate electrode 22 that is a saddle fin typeburied word line, the buried insulating film 24, the first impuritydiffusion region 28, and the second impurity diffusion region 29.

As shown in FIGS. 2A and 2B, the first and second transistors 19-1 and19-2 are arranged to be adjacent to each other. The second impuritydiffusion region 29 functions as an impurity diffusion region (drainregion in the case of the structure shown in FIGS. 2A and 2B) that iscommon to the first and second transistors 19-1 and 19-2.

That is, the second side 18 b of the gate electrode groove 18 that formsthe first transistor 19-1 and the second side 18 b of the gate electrodegroove 18 that forms the second transistor 19-2 are configured to faceeach other through the second impurity diffusion region 29.

Referring to FIGS. 2A to 2C, the gate insulating film 21 is provided tocover the first and second sides 18 a and 18 b of the gate electrodegroove 18 and the bottom portion 18 c of the gate electrode groove 18.The gate insulating film 21 is provided to cover the surface (that is,the upper portion 15 a and the pair of facing sides 15 b and 15 c) ofthe fin portion 15 provided in the bottom portion 18 c of the gateelectrode groove 18.

As the gate insulating film 21, a silicon oxide film (SiO₂ film) of asingle layer, a silicon oxynitride film (SiON film), a stacked siliconoxide film (SiO₂ film), and a stacked film obtained by stacking asilicon nitride film (SiN film) on a silicon oxide film (SiO₂ film) maybe used.

When the silicon oxide film (SiO₂ film) of the single layer is used asthe gate insulating film 21, the thickness of the gate insulating film21 may be set to 6 nm.

Referring to FIGS. 2A to 2C, the gate electrode 22 adopts the saddle fintype buried word line to decrease the OFF leak current and improve thewriting characteristic. Because the S factor may be decreased byadopting the saddle fin type, a threshold voltage may be decreased whilethe OFF leak current is maintained. Because the current drivingcapability may be improved by adopting the saddle fin type, the writingcharacteristic may be improved.

The gate electrode 22 is arranged to bury a lower portion of the gateinsulating groove 18 through the gate insulating film 21. Thereby, thegate electrode 22 is provided to step over the fin portion 15 throughthe gate insulating film 21. The top surface 22 a of the gate electrode22 is arranged at a position lower than the main surface 13 a of thesemiconductor substrate 13. The gate electrode 22 may have a stackedstructure in which a titanium nitride film and a tungsten film aresequentially stacked.

In the semiconductor device according to this embodiment, the thresholdvoltages of the first and second transistors 19-1 and 19-2 may beappropriately adjusted by adjusting the thickness of the gate insulatingfilm 21 and a work function of the gate electrode 22. In the saddle fintype cell transistor, the threshold voltage is preferably set in a rangeof 0.5 to 1.0 V. In this case, if the threshold voltage is less than 0.5V, the off leak current increases and the information retentioncharacteristic is deteriorated.

Meanwhile, if the threshold voltage is more than 1.0 V, this is notpreferable because the current driving capability is lowered, writing ofinformation becomes insufficient, and the information retentioncharacteristic is deteriorated.

Specifically, if the equivalent oxide thickness of the gate insulatingfilm 21 is set within a range of 4 to 6 nm and the work function of thegate electrode 22 is set within a range of 4.6 to 4.8 eV, the thresholdvoltage of one of or both the first and second transistors 19-1 and 19-2may be set to 0.8 to 1.0 V.

Referring to FIGS. 2A and 2B, the buried insulating film 24 is arrangedto bury the gate electrode groove 18 provided with the gate insulatingfilm 21, to cover the top surface 22 a of the gate electrode 22.

The upper portion of the buried insulating film 24 protrudes more thanthe main surface 13 a of the semiconductor substrate 13 and the topsurface 24 a of the protruding portion is flush with the top surface 26a of the mask insulating film 26. As the buried insulating film 24, asilicon oxide film (SiO₂ film) may be used.

Referring to FIGS. 2A and 2B, the mask insulating film 26 is provided onthe top surface 28 a of the first impurity diffusion region 28. The maskinsulating film 26 has an opening 26A having a groove shape that isformed on the second element isolation groove 54. The mask insulatingfilm 26 functions as an etching mask when the second element isolationgroove 54 is formed in the semiconductor substrate 13 by anisotropicetching. As the mask insulating film 26, a silicon nitride film may beused. In this case, the thickness of the mask insulating film 26 may beset to 50 nm.

Referring to FIGS. 2A and 2B, the first impurity diffusion region 28 isprovided in the semiconductor substrate 13 positioned at the side of thefirst side 18 a, to cover the upper portion 21A of the gate insulatingfilm 21 formed in the first side 18 a of the gate electrode groove 18.

That is, the first side 18 a of the gate electrode groove 18 that formsthe first transistor 19-1 and the first side 18 a of the gate electrodegroove 18 that forms the second transistor 19-2 are configured to facethe sides of the second element isolation grooves 54 through thesemiconductor substrate 13, respectively.

Therefore, the first impurity diffusion region 28 is provided to includethe top surface 13 a of the semiconductor substrate 13 interposedbetween the first side 18 a and the second element isolation groove 54and cover the upper portion 21A of the gate insulating film 21 formed onthe first side 18 a.

The bottom surface 28 b of the first impurity diffusion region 28 isarranged at a position higher than the top surface 22 a of the gateelectrode 22 buried in the gate electrode groove 18 (position of theside of the top surface 13 a of the semiconductor substrate 13). Thedistance between a horizontal line including the bottom surface 28 b ofthe first impurity diffusion region 28 and a horizontal line includingthe top surface 22 a of the buried gate electrode 22 is preferably in arange of 5 to 10 nm. If the distance is less than 5 nm, the currentdriving capacity may be lowered and the writing characteristic may bedeteriorated. Meanwhile, if the distance is more than 10 nm, thejunction electric field may increase and the information retentioncharacteristic may be deteriorated.

The first impurity diffusion region 28 is provided with respect to eachof the gate electrodes 22 forming the first and second transistors 19-1and 19-2.

The first impurity diffusion region 28 is an impurity diffusion regionthat functions as a source/drain region (source region in the case ofthe structure shown in FIGS. 2A and 2B) of each of the first and secondtransistors 19-1 and 19-2. When the semiconductor substrate 13 is ap-type silicon substrate, the first impurity diffusion region 28 isformed by ion-implanting n-type impurities into the semiconductorsubstrate 13.

Referring to FIGS. 2A and 2B, the second impurity diffusion region 29 isprovided in a portion of the semiconductor substrate 13 that is arrangedbetween the two gate electrode grooves 18. Specifically, the secondimpurity diffusion region 29 is provided such that the depth thereof isless than the depth of the bottom portion 18 c of the gate electrodegroove 18 and is more than the depth of the top portion of the finportion 15 (portion of the top surface 15 a closest to the surface 13 aof the semiconductor substrate 13). That is, the bottom portion of thesecond impurity diffusion region 29 is positioned between the topportion of the top surface 15 a of the fin portion 15 and the bottomportion 18 c of the gate electrode groove 18. In other words, withrespect to the junction position between the second impurity diffusionregion 29 (for example, n-type diffusion region) and the semiconductorsubstrate 13 (for example, p-type channel), the lower limit of the depthis set as the position of the top portion of the fin portion 15 and theupper limit of the depth is set as the position of the bottom portion 18c of the gate electrode groove 18. Thereby, the second impuritydiffusion region 29 is arranged to cover all of the portions other thana lower end of the gate insulating film 21 provided in the second side18 b of each of the two gate electrode grooves 18.

In this case, if the depth of the second impurity diffusion region 29 isless than the depth of the top portion of the fin portion 15, thedisturbance failure becomes remarkable. Meanwhile, if the depth of thesecond impurity diffusion region 29 is more than the depth of the bottomportion 18 c of the gate electrode groove 18, the voltage may be lowerthan the predetermined threshold voltage (Vt), because the dopedimpurities (for example, n-type impurities) reach the fin portion 15. Ifthe channel concentration of the semiconductor substrate 13 (forexample, concentration of the p-type impurities) is increased tocompensate for the decrease in the threshold voltage (Vt), the strengthof the electric field in the junction between the first impuritydiffusion region 28 (for example, n-type diffusion layer) and thesemiconductor substrate 13 (for example, p channel) increases and theinformation retention characteristic is remarkably deteriorated (referto FIG. 19).

The second impurity diffusion region 29 is an impurity diffusion regionthat functions as a source/drain region (drain region in the case of thestructure shown in FIG. 2) common to the first and second transistors19-1 and 19-2. When the semiconductor substrate 13 is a p-type siliconsubstrate, the second impurity diffusion region 29 is formed byion-implanting the n-type impurities into the semiconductor substrate13. Thereby, the fin portion 15 becomes a p-type.

FIG. 20 is a relation diagram showing a junction position of eachimpurity diffusion region in the semiconductor device 10 according tothis embodiment. In FIG. 20, a horizontal axis shows the depth from thesurface 13 a of the semiconductor substrate 13 and a vertical axis showsan impurity concentration of each of the semiconductor substrate 13 andthe first and second impurity diffusion regions 28 and 29. In FIG. 20,an intersection of each profile of the first and second impuritydiffusion regions 28 and 29 and a profile of the semiconductor substrate13 becomes a metallurgical junction position.

FIG. 20 shows a relation among the depth of the gate electrode groove18, the height H of the fin portion 15, and the junction position of thesecond impurity diffusion region 29.

As such, in the semiconductor device 10 according to this embodiment,the fin portion 15 is provided in the bottom portion 18 c of the gateelectrode groove 18 and the first impurity diffusion region 28 thatincludes the top surface 13 a of the semiconductor substrate 13interposed between the first side 18 a and the second element isolationgroove 54 and covers the upper portion 21A of the gate insulating film21 arranged on the first side 18 a and the second impurity diffusionregion 29 that is arranged in the portion of the semiconductor substrate13 positioned between the two gate electrode grooves 18 and covers allof the portions other than the lower end of the gate insulating film 21arranged on the second side 18 b of the pair of gate electrode grooves18 are provided. Thereby, when the first and second transistors 19-1 and19-2 are operated, the first channel region is formed in the fin portion15, the second channel region is formed in the portions of thesemiconductor substrate 13 that contacts the lower portion of the gateinsulating film 21 arranged on the first side 18 a, contacts the bottomportion 18 c of the gate electrode groove 18, and is positioned at alower side of the bottom portion of the second impurity diffusion region29 arranged on the second side 18 b, and the channel region is notprovided in the portion of the semiconductor substrate 13 that contactsthe second side 18 b and is positioned at the upper side of the bottomportion of the second impurity diffusion region 29.

In other words, the channel region is configured of the fin portion 15covered to step over the gate electrode through the gate insulating film21 and three surfaces constituting the gate electrode groove 18.

That is, when the first and second transistors 19-1 and 19-2 are turnedon, the fin portion 15 is fully depleted. Therefore, in the first andsecond transistors 19-1 and 19-2, the resistance becomes low and thecurrent can easily flow, as compared with the transistors according tothe related art. Thereby, in a miniaturized memory cell, the channelresistance may be decreased and the on-state current may be increased.

When one of the first and second transistors 19-1 and 19-2 is operated,the other transistor may be suppressed from being erroneously operated.

Therefore, even when the size of the semiconductor device 10 isdecreased and the gate electrodes 22 are arranged at a narrow pitch, thefirst and second transistors 19-1 and 19-2 may be operated independentlyand stably.

The fin portion 15 is provided in the bottom portion 18 c of each of thetwo gate electrode grooves 18 arranged to be adjacent to each other andthe depth H of the fin portion 15 is set to 40 nm or less. Thus, in thestate in which “L” is stored in the lower electrode 57 electricallyconnected to the first transistor 19-1 and “H” is stored in the lowerelectrode 57 electrically connected to the second transistor 19-2, whenon/off of the gate electrode 22 (word line) corresponding to the firsttransistor 19-1 is repeated, the fin portion 15 becoming the channelregion of the first transistor 19-1 is a p-type and it becomes difficultto induce the electrons e⁻ (not shown in the drawings). Therefore, theelectrons e⁻ induced in the channel of the first transistor 19-1 may besuppressed from reaching the second impurity diffusion region 28 (drainregion) forming the second transistor 19-2.

Thereby, the electrons e⁻ induced in the channel of the first transistor19-1 may be prevented from destroying H information stored in the lowerelectrode 57 electrically connected to the second transistor 19-2 tochange the state to the L state. Therefore, generation of thedisturbance failure in which the operation state of one adjacent cellchanges a storage state of the other cell may be suppressed.

In the DRAM in which the interval between the two gate electrodes 22arranged to be adjacent to each other is 50 nm or less, the generationof the disturbance failure may be suppressed.

Referring to FIGS. 2A and 2B, the opening 32 is formed between theburied insulating films 24 protruding from the two gate electrodegrooves 18. The opening 32 is formed to expose the top surface 29 a ofthe second impurity diffusion region 29.

Referring to FIGS. 2A and 2B, the bit line contact plug 33 is providedto bury the opening 32 and is configured integrally with the bit line34. The lower end of the bit line contact plug 33 contacts the topsurface 29 a of the second impurity diffusion region 29. When the bitline 34 is configured using a stacked film obtained by sequentiallystacking a polysilicon film, a titanium nitride (TiN) film, and atungsten (W) film, the bit line contact plug 33 may be configured usingthe polysilicon film.

Referring to FIGS. 2A and 2B, the bit line 34 is provided on a topsurface 24 a of the buried insulating film 24 and is configuredintegrally with the bit line contact plug 33. Thereby, the bit line 34is electrically connected to the second impurity diffusion region 29through the bit line contact plug 33.

As the material of the bit line 34, a stacked film obtained bysequentially stacking a polysilicon film, a titanium nitride film, and atungsten film, the polysilicon film, or the titanium nitride film may beused.

Referring to FIGS. 2A and 2B, the cap insulating film 36 is provided tocover the top surface of the bit line 34. The cap insulating film 36protects the top surface of the bit line 34 and functions as an etchingmask when a base material becoming the bit line 34 is patterned byanisotropic etching (specifically, dry etching). As the cap insulatingfilm 36, a stacked film that is obtained by sequentially stacking asilicon nitride film (SiN film) and a silicon oxide film (SiO₂ film) maybe used.

Referring to FIGS. 2A and 2B, the sidewall film 37 is provided to covera side of the bit line 34. The sidewall film 37 has a function forprotecting the sidewall of the bit line 34. As the sidewall film 37, astacked film that is obtained by sequentially stacking a silicon nitridefilm (SiN film) and a silicon oxide film (SiO₂ film) may be used.

Referring to FIGS. 2A and 2B, the interlayer insulating film 38 isprovided on the top surface 26 a of the mask insulating film 26 and thetop surface 55 a of the second element isolation insulating film 55. Atop surface 38 a of the interlayer insulating film 38 is flush with atop surface 36 a of the cap insulating film 36. As the interlayerinsulating film 38, a silicon oxide film (SiO₂ film) formed by a CVDmethod or a coating-based insulating film (silicon oxide film (SiO₂film)) formed by an SOG method may be used.

Referring to FIGS. 2A and 2B, a contact hole 41 is formed in the buriedinsulating film 24, the mask insulating film 26, and the interlayerinsulating film 38 to expose a part of the top surface 28 a of the firstimpurity diffusion region 28.

Referring to FIGS. 2A and 2B, the capacitor contact plug 42 is providedto bury the contact hole 41. The lower end of the capacitor contact plug42 contacts a part of the top surface 28 a of the first impuritydiffusion region 28. Thereby, the capacitor contact plug 42 iselectrically connected to the first impurity diffusion region 28. A topsurface 42 a of the capacitor contact plug 42 is flush with the topsurface 38 a of the interlayer insulating film 38. The capacitor contactplug 42 may have a stacked structure that is obtained by sequentiallystacking a titanium nitride film and a tungsten film.

Referring to FIGS. 2A and 2B, a capacitor contact pad 44 is provided onthe top surface 38 a of the interlayer insulating film 38, such that apart thereof is connected to the top surface 42 a of the capacitorcontact plug 42. The lower electrode 57 that forms the capacitor 48 isconnected to an upper side of the capacitor contact pad 44. Thereby, thecapacitor contact pad 44 electrically connects the capacitor contactplug 42 and the lower electrode 57.

Referring to FIG. 1, the capacitor contact pad 14 is formed in acircular shape and is arranged at a position different from the positionof the capacitor contact plug 42 in the Y direction. The capacitorcontact pad 44 is arranged between the adjacent bit lines 34 in the Xdirection.

That is, the capacitor contact pads 44 are arranged at the differentpositions such that the center portions of the capacitor contact pads 44are repetitively arranged on every other gate electrode 22 along the Ydirection or the side of every other gate electrode 22 along the Ydirection. In other words, the capacitor contact pads 44 are arranged ina zigzag shape in the Y direction.

Referring to FIGS. 2A and 2B, the silicon nitride film 46 is provided onthe top surface 38 a of the interlayer insulating film 38 to surround anouter circumferential portion of the capacitor contact pad 44.

The capacitor 48 is provided with respect to each capacitor contact pad44.

One capacitor 48 has one lower electrode 57, a capacitor insulating film58 common to the plurality of lower electrodes 57, and an upperelectrode 59 to be an electrode common to the plurality of lowerelectrodes 57.

The lower electrode 57 is provided on the capacitor contact pad 44 andis connected to the capacitor contact pad 44. The lower electrode 57 isformed in a coronal shape.

The capacitor insulating film 58 is provided to cover surfaces of theplurality of lower electrodes 57 exposed from the silicon nitride film46 and a top surface of the silicon nitride film 46.

The upper electrode 59 is provided to cover the surface of the capacitorinsulating film 58. The upper electrode 59 is arranged to bury an innerportion of the lower electrode 57 provided with the capacitor insulatingfilm 58 and gaps between the plurality of lower electrodes 57. A topsurface 59 a of the upper electrode 59 is arranged on an upper side ofupper ends of the plurality of lower electrodes 57.

The capacitor 48 that has the above-described configuration iselectrically connected to the first impurity diffusion region 28 throughthe capacitor contact pad 44.

An interlayer insulating film (not shown in the drawings) that coversthe top surface 59 a of the upper electrode 59, a contact plug (notshown in the drawings) that is provided in the interlayer insulatingfilm, and a wiring (not shown in the drawings) that is connected to thecontact plug may be provided.

The semiconductor device 10 according to the embodiment of the presentinvention has the following configuration. The semiconductor device 10includes a plurality of first element isolation regions 14 that areformed of the semiconductor substrate 13, are provided in thesemiconductor substrate 13 to extend in the first direction, andpartition the active region 16 having the plurality of element formationregions R, a plurality of second element isolation regions 17 that areprovided in the semiconductor substrate 13 to extend in the seconddirection crossing the first direction and partition the active region16 in the plurality of element formation regions R, a pair of gateelectrode grooves 18 that are provided to extend in the second directioncrossing the first element isolation region 14 and the active region 16in the surface layer of the semiconductor substrate 13 between thesecond element isolation regions 17 to be adjacent to each other andhave the first and second sides 18 a and 18 b facing each other and thebottom portion 18 c, a fin portion 15 that is formed such that a part ofthe active region 16 protrudes from the bottom portion 18 c of the gateelectrode groove 18, by setting the depth of the second groove portion18B formed in the first element isolation region 14 to be more than thedepth of the first groove portion 18A of the gate electrode groove 18formed in the active region 16 and setting the depth of the portion ofthe first groove portion 18A facing the second groove portion 18B to bealmost equal to the depth of the second groove portion 18B, the gateinsulating film 21 that covers the gate electrode groove 18 and thesurface of the fin portion 15, a pair of gate electrodes 22 that areburied in the lower portions of the pair of gate electrode grooves 18and are formed to step over the fin portion 15 through the gateinsulating film 21, two first impurity diffusion regions 28 that areprovided on the top surface 13 a of the semiconductor substrate 13between the second element isolation region 17 and the gate electrodegroove 18 and are connected to the capacitors 48, and one secondimpurity diffusion region 29 that is provided in the semiconductorsubstrate 13 between the pair of gate electrode grooves 18 arranged suchthat the second sides 18 b face each other and is connected to the bitline 34. The element formation region R has the first transistor 19-1and the second transistor 19-2 that share the second impurity diffusionregion 29. The first transistor 19-1 is configured of at least one ofthe gate electrodes 22, the fin portion 15, and one of the firstimpurity diffusion regions 28 and the second transistor 19-2 isconfigured of at least the other of the gate electrodes 22, the finportion 15, and the other of the first impurity diffusion regions 28.The depth of the bottom portion 18 c of the gate electrode groove 18 is150 to 200 nm from the surface 13 a of the semiconductor substrate 13and the height from the bottom portion 18 c of the gate electrode groove18 to the top portion (upper portion) of the fin portion 15 is 10 to 40nm.

The second impurity diffusion region 29 is provided such that the depththereof is less than the depth of the bottom portion 18 c of the gateelectrode groove 18 and is more than the depth of the top portion (upperportion) of the fin portion 15.

According to the semiconductor device 10 according to this embodiment,the fin portion 15 is provided in the bottom portion 18 c of the gateelectrode groove 18. The first impurity diffusion region 28 thatincludes the top surface 13 a of the semiconductor substrate 13interposed between the first side 18 a and the second element isolationgroove 54 and covers the upper portion 21A of the gate insulating film21 arranged on the first side 18 a and the second impurity diffusionregion 29 that is arranged in the portion of the semiconductor substrate13 positioned between the two gate electrode grooves 18 and covers allof the portions other than the lower end of the gate insulating film 21arranged on the second sides 18 b of the pair of gate electrode grooves18 are provided. Thereby, when the first and second transistors 19-1 and19-2 are operated, the first channel region is formed in the fin portion15, the second channel region is formed in the portions of thesemiconductor substrate 13 that contacts the lower portion of the gateinsulating film 21 arranged on the first side 18 a, contacts the bottomportion 18 c of the gate electrode groove 18, and is positioned at thelower side of the bottom portion of the second impurity diffusion region29 arranged on the second side 18 b, and the channel region is notprovided in the portion of the semiconductor substrate 13 that contactsthe second side 18 b and is positioned at the upper side of the bottomportion of the second impurity diffusion region 29.

In other words, the channel region may be configured of the fin portion15 that is covered to step over the gate electrode 22 through the gateinsulating film 21 and the three surfaces that form the gate electrodegroove 18.

That is, when the first and second transistors 19-1 and 19-2 are turnedon, the fin portion 15 is fully depleted. Therefore, in the first andsecond transistors 19-1 and 19-2, the resistance becomes low and thecurrent can easily flow, as compared with the transistors according tothe related art. Thereby, in the miniaturized memory cell, the channelresistance may be decreased and the on-state current may be increased.

When one of the first and second transistors 19-1 and 19-2 is operated,the other transistor may be suppressed from being erroneously operated.

Therefore, even when the size of the semiconductor device 10 isdecreased and the gate electrodes 22 are arranged at a narrow pitch, thefirst and second transistors 19-1 and 19-2 may be operated independentlyand stably.

The fin portion 15 is provided in the bottom portion 18 c of each of thetwo gate electrode grooves 18 arranged to be adjacent to each other andthe depth H of the fin portion 15 is set to 40 nm or less. Thus, in thestate in which “L” is stored in the lower electrode 57 electricallyconnected to the first transistor 19-1 and “H” is stored in the lowerelectrode 57 electrically connected to the second transistor 19-2, whenon/off of the gate electrode 22 (word line) corresponding to the firsttransistor 19-1 is repeated, the fin portion 15 becoming the channelregion of the first transistor 19-1 is a p-type and it becomes difficultto induce the electrons e⁻ (not shown in the drawings). For this reason,the electrons e⁻ induced in the channel of the first transistor 19-1 maybe suppressed from reaching the second impurity diffusion region 28(drain region) forming the second transistor 19-2.

Thereby, the electrons e⁻ induced in the channel of the first transistor19-1 may be prevented from destroying H information stored in the lowerelectrode 57 electrically connected to the second transistor 19-2 tochange the state to the L state. Therefore, generation of thedisturbance failure in which the operation state of one adjacent cellchanges a storage state of the other cell may be suppressed.

In the DRAM in which the interval between the two gate electrodes 22arranged to be adjacent to each other is 50 nm or less, the generationof the disturbance failure may be suppressed.

The gate electrode 22 that is arranged to bury the lower portion of thegate electrode groove 18 through the gate insulating film 21 and theburied insulating film 24 that is arranged to bury the gate electrodegroove 18 and covers the top surface 22 a of the gate electrode 22 areprovided and the gate electrode 22 may be prevented from protruding tothe upper side of the surface 13 a of the semiconductor substrate 13.

Thereby, in this embodiment, when the DRAM is used as the semiconductordevice 10, the bit line 34 or the capacitor 48 that is formed in theprocess after the process for forming the gate electrode 22 may beeasily formed. Therefore, the semiconductor device 10 may be easilymanufactured.

Referring to FIGS. 3A to 3D, 4A to 4D, 5A to 5D, 6A to 6D, 7A to 7D, 8Ato 8D, 9A to 9D, 10A to 10C, 11A to 11C, 12A to 12C, 13A to 13C, 14, 15,and 16, a method of manufacturing the semiconductor device 10(specifically, a memory cell array 11) according to this embodiment willbe described.

In this case, a line A-A shown in FIGS. 3A to 13A corresponds to a lineA-A shown in FIG. 1 and a line B-B shown in FIGS. 3B to 13B correspondsto a line B-B shown in FIG. 1.

Cross-sections taken along a line C-C shown in FIGS. 3A to 9A are shownin FIGS. 3D to 9D, respectively. The cross-section taken along the lineC-C shows a cross-section along an extension direction of the gateelectrode 22 that is the buried word line in the semiconductor device 10according to this embodiment.

First, in the processes shown in FIGS. 3A to 3D, a pad oxide film 65 isformed on the main surface 13 a of the semiconductor substrate 13. Next,a silicon nitride film 66 having an opening 66 a of a groove shape isformed on the pad oxide film 65.

As shown in FIGS. 3A and 3B, the openings 66 a extend in a stripe shapein a direction (first direction) inclined with respect to the Xdirection by the predetermined angle and are formed at the predeterminedinterval in the Y direction.

At this time, the opening 66 a is formed to expose a top surface of thepad oxide film 65 corresponding to a formation region of the firstelement isolation groove 51. The opening 66 a is formed by forming apatterned photoresist (not shown in the drawings) on the silicon nitridefilm 66 and etching the silicon nitride film 66 by anisotropic etchingusing the photoresist as a mask. The photoresist is removed after theopening 66 a is formed.

Next, the first element isolation groove 51 that extends in the firstdirection is formed by etching the semiconductor substrate 13 byanisotropic etching (dry etching) using the silicon nitride film 66having the opening 66 a as a mask.

A width W₁ of the first element isolation groove 51 may be set to 43 nm.The depth D₁ of the first element isolation groove 51 (depth from themain surface 13 a of the semiconductor substrate 13) may be set to 250nm.

Next, in the processes shown in FIGS. 4A to 4D, a first elementisolation insulating film 52 that buries the first element isolationgroove 51 is formed.

Specifically, the first element isolation groove 51 is buried by asilicon oxide film (SiO₂ film) formed by a high density plasma (HDP)method or a coating-based silicon oxide film (SiO₂ film) formed by aspin on glass (SOG) method.

Next, the silicon oxide film (SiO₂ film) that is formed on the upperside of the top surface of the silicon nitride film 66 is removed by achemical mechanical polishing (CMP) method to form the first elementisolation insulating film 52 formed of the silicon oxide film (SiO₂film) in the first element isolation groove 51.

Thereby, the first element isolation region 14 that includes the firstelement isolation groove 51 and the first element isolation insulatingfilm 52 and partitions the active region 16 of the stripe shapeextending in the first direction is formed.

Next, in the processes shown in FIGS. 5A to 5D, the silicon nitride film66 shown in FIGS. 4A to 4D is removed and the pad oxide film 65 isremoved. Specifically, the silicon nitride film 66 is removed by hotphosphoric acid and the pad oxide film 65 is removed by a hydrogenfluoride (HF)-based etching liquid. Thereby, the active region 16 havingthe stripe shape is exposed.

Next, the portion of the first element isolation insulating film 52 thatprotrudes from the main surface 13 a of the semiconductor substrate 13is removed to make the top surface 52 a of the first element isolationinsulating film 52 flush with the main surface 13 a of the semiconductorsubstrate 13. The first element isolation insulating film 52 thatprotrudes from the main surface 13 a of the semiconductor substrate 13is removed by wet etching.

Next, in the processes shown in FIGS. 6A to 6D, the mask insulating film26 that has the opening 26A of the groove shape is formed on the mainsurface 13 a of the semiconductor substrate 13 and the top surface 52 aof the first element isolation insulating film 52 shown in FIGS. 5A to5D.

Specifically, the mask insulating film 26 is formed as follow. A siliconnitride film (base material of the mask insulating film 26) that coversthe main surface 13 a of the semiconductor substrate 13 and the topsurface 52 a of the first element isolation insulating film 52 isformed. Next, a patterned photoresist (not shown in the drawings) isformed on the silicon nitride film and the opening 26A is formed in themask insulating layer 26 by anisotropic etching using the photoresist asa mask.

At this time, a plurality of openings 26A extend in the Y direction(second direction) and are formed at the predetermined interval withrespect to the X direction (refer to FIG. 6A). The opening 26A is formedto expose the main surface 13 a of the semiconductor substrate 13corresponding to a formation region of the second element isolationgroove 54. The photoresist (not shown in the drawings) is removed afterthe opening 26A is formed.

Next, the second element isolation groove 54 that extends in the firstdirection is formed by etching the semiconductor substrate 13 byanisotropic etching (dry etching) using the mask insulating film 26having the opening 26 a as a mask.

A depth D₂ of the second element isolation groove 54 (depth from themain surface 13 a of the semiconductor substrate 13) may be set to 250nm.

Next, the second element isolation insulating film 55 that buries thesecond element isolation groove 54 is formed.

Specifically, the second element isolation groove 54 is buried by asilicon oxide film (SiO₂ film) formed by an HDP method or acoating-based silicon oxide film (SiO₂ film) formed by an SOG method.

Next, the insulating film that is formed on the upper side of the topsurface 26 a of the mask insulating film 26 is removed by the CMP methodto form the second element isolation insulating film 55 formed of thesilicon oxide film (SiO₂ film) and having the top surface 55 a flushwith the top surface 26 a of the mask insulating film 26 in the secondelement isolation groove 54.

Thereby, the second element isolation region 17 that includes the secondelement isolation groove 54 and the second element isolation insulatingfilm 55 and partitions the active region 16 of the stripe shape shown inFIGS. 5A to 5D into the plurality of element formation regions R isformed.

As such, after the first element isolation region 14 including the firstelement isolation groove 51 formed in the semiconductor substrate 13 andthe first element isolation insulating film 52 burying the first elementisolation groove 51 and partitioning the active region 16 having thestripe shape is formed, the second element isolation region 17 includingthe second element isolation groove 54 formed in the semiconductorsubstrate 13 and the second element isolation insulating film 55 buryingthe second element isolation groove 54 and partitioning the plurality ofelement formation regions R is formed. As a result, as compared with thecase in which a dummy gate electrode (not shown in the drawings) towhich negative potential is applied is provided in the second elementisolation groove 54 through the gate insulating film 21 and theplurality of element formation regions R are partitioned, the potentialof the dummy gate electrode does not exert a bad influence upon thefirst and second transistors 19-1 and 19-2 (refer to FIG. 2). Therefore,the first and second transistors 19-1 and 19-2 may be easily turned onand a retention characteristic of the data of the memory cell array 11may be improved.

Next, in the processes shown in FIGS. 7A to 7D, the two openings 26Bhaving the groove shape that extend in the Y direction are formed in themask insulating film 26 positioned between the two second elementisolation regions 17.

At this time, the opening 26B is formed to expose the main surface 13 aof the semiconductor substrate 13 corresponding to a formation region ofthe gate electrode groove 18. The opening 26B is formed by forming apatterned photoresist (not shown in the drawings) on the mask insulatingfilm 26 and etching the mask insulating film 26 by anisotropic etching(specifically, dry etching) using the photoresist as a mask. Thephotoresist is removed after the opening 26B is formed.

Next, as shown in FIG. 7D, first, the element isolation insulating film52 that forms the first element isolation region 14 is selectivelyetched by anisotropic etching (specifically, dry etching) using the maskinsulating film 26 having the opening 26B as a mask. Thereby, the secondgroove portion 18B of the gate electrode groove 18 is formed in thefirst element isolation region 14. In this case, the second grooveportion 18B is formed such that a depth D₄ thereof (depth from the mainsurface 13 a of the semiconductor substrate 13 (not shown in thedrawings)) is less than the depths D₁ and D₂ of the first and secondelement isolation grooves 51 and 54. Specifically, the depth D₄ of thesecond groove portion 18B may be set in a range of 150 to 200 nm whenthe depths D₁ and D₂ of the first and second element isolation grooves51 and 54 are 250 nm.

Next, the semiconductor substrate 13 that forms the active region 16 isselectively etched. Thereby, the first groove portion 18A of the gateelectrode groove 18 is formed in the active region 16. In this case, thefirst groove portion 18A is formed such that a depth D₃ thereof (depthfrom the main surface 13 a of the semiconductor substrate 13) is lessthan the depth D₄ of the second groove portion 18B. Specifically, thefirst groove portion 18A is formed such that the depth D₃ thereof isless than the depth D₄ of the second groove portion 18B by 10 to 40 nm.The depth D₄ of the gate electrode groove 18 may be set to 150 nm whenthe depths D₁ and D₂ of the first and second element isolation grooves51 and 54 are 250 nm.

Next, in the processes shown in FIGS. 8A to 8D, the portion of the firstgroove portion 18A forming the gate electrode groove 18 facing thesecond groove portion 18B is selectively etched by isotropic etching(specifically, dry wet etching) using the mask insulating film 26 havingthe opening 26B as a mask, until the depth of the portion becomes almostequal to the depth of the second groove portion 18B.

In this way, the first groove portion 18A of the gate electrode groove18 that is formed in the active region 16 may be formed such that thedepth of the end facing the second groove portion 18B becomes equal tothe depth (that is, D₄) of the second groove portion 18B (refer to FIGS.8C and 8D). Meanwhile, the first groove portion 18A may be formed suchthat the depth of the center portion becomes D₃ (refer to FIGS. 8B and8D). That is, the gate electrode groove 18 that has the first and secondsides 18 a and 18 b and the bottom portion 18 c and the fin portion 15that is provided such that a part of the active region 16 protrudes fromthe bottom portion 18 c may be formed.

Next, in the processes shown in FIGS. 9A to 9D, the gate insulating film21 that covers the surfaces of each gate electrode groove 18 (that is,the first and second sides 18 a and 18 b and the bottom portion 18 c ofthe gate electrode groove 18) and the surface of the fin portion 15(that is, the upper portion 15 a and the pair of facing sides 15 b and15 c) is formed.

As the gate insulating film 21, a silicon oxide film (SiO₂ film) of asingle layer, a silicon oxynitride film (SiON film), a stacked siliconoxide film (SiO₂ film), and a stacked film obtained by stacking asilicon nitride film (SiN film) on a silicon oxide film (SiO₂ film) maybe used.

When the silicon oxide film (SiO₂ film) of the single layer is used asthe gate insulating film 21, the gate insulating film 21 may be formedby a heat oxidation method. In this case, the thickness of the gateinsulating film 21 may be set to 6 nm.

Next, the gate electrode 22 that buries the lower portion of the gateelectrode groove 18 to step over each fin portion 15 through the gateinsulating film 21 is formed such that the top surface 22 a becomeslower than the main surface 13 a of the semiconductor substrate 13(refer to FIG. 9D).

Specifically, a titanium nitride film and a tungsten film aresequentially stacked by a CVD method to bury the gate electrode groove18. Next, the titanium nitride film and the tungsten film areblanket-etched by dry etching such that the titanium nitride film andthe tungsten film remain on the lower portion of the gate electrodegroove 18 and the gate electrode 22 that includes the titanium nitridefilm and the tungsten film is formed. Each gate electrode 22 forms aword line of the memory cell.

Next, the buried insulating film 24 that covers the top surface 22 a ofthe gate electrode 22 and buries the gate electrode groove 18 and theopening 26B having the groove shape is formed.

Specifically, the upper portion of the gate electrode groove 18 and theopening 26B are buried by an insulating film (for example, silicon oxidefilm (SiO₂ film)) formed by an HDP method or a coating-based insulatingfilm (for example, silicon oxide film (SiO₂ film)) formed by an SOGmethod.

Next, the insulating film that is formed on the upper side of the topsurface 26 a of the mask insulating film 26 is removed by a CMP method.Thereby, the buried insulating film 24 that is formed of the insulatingfilm (for example, silicon oxide film (SiO₂ film)) burying the gateelectrode groove 18 and the opening 26B and has the top surface 24 aflush with the top surface 26 a of the mask insulating film 26 isformed.

Because the saddle fin type gate electrode 22 that becomes the buriedword line is formed by the processes shown in FIGS. 3D to 9D, thedescription of the cross-sectional views taken along the line C-C shownin FIGS. 3A to 9A is omitted.

Next, in the processes shown in FIGS. 10A to 10C, phosphorus (P) ision-implanted as an n-type impurity (conductive impurity different froma p-type silicon substrate to be the semiconductor substrate 13) into anentire top surface of the structure shown in FIGS. 9A to 9C, underconditions in which energy is 100 KeV and a dose amount is 1E14atoms/cm², the first impurity diffusion region 28 is formed in thesemiconductor substrate 13 positioned between the gate electrode groove18 and the first element isolation region 17, and the impurity diffusionregion 71 that becomes a part of the second impurity diffusion region 29is formed in the semiconductor substrate 13 positioned between the twogate electrode grooves 18.

Thereby, the first impurity diffusion region 28 is formed in thesemiconductor substrate 13 positioned at the side of the first side 18 aof the gate electrode groove 18 to cover the upper portion 21A of thegate insulating film 21 formed on the first side 18 a.

At this time, the first impurity diffusion region 28 is formed toinclude the top surface 13 a of the semiconductor substrate 13interposed between the first side 18 a and the second element isolationgroove 54 and have the bottom surface 28 b at a position higher than thetop surface 22 a of the buried gate electrode 22.

In this step, the thickness of the mask insulating film 26 may be set to50 nm.

Next, in the processes shown in FIGS. 11A to 11C, a photoresist 73 thathas an opening 73 a of the groove shape exposing the top surface 26 a ofthe mask insulating film 26 positioned between the buried insulatingfilms 24 is formed on the top surface 24 a of the buried insulating film24, the top surface 26 a of the mask insulating film 26, and the topsurface 55 a of the second element isolation insulating film 55.

Next, the mask insulating film 26 that is exposed from the opening 73 ais removed by the etching (wet etching or dry etching) using thephotoresist 73 as a mask.

Thereby, the top surface 71 a of the impurity diffusion region 71 isexposed and a part of the top surface 52 a of the first elementisolation insulating film 52 that is flush with the top surface 71 a ofthe impurity diffusion region 71 is exposed.

Next, in the processes shown in FIGS. 12A to 12C, phosphorus (P) isselectively ion-implanted as an n-type impurity (conductive impuritydifferent from a p-type silicon substrate as the semiconductor substrate13) into the impurity diffusion region 71 (in other words, thesemiconductor substrate 13 where the impurity diffusion region 71 isformed) exposed from the photoresist 73, and the second impuritydiffusion region 29 is formed in the semiconductor substrate 13positioned between the two gate electrode grooves 18, such that thedepth of the bottom portion becomes the depth between the top portion ofthe top surface 15 a of the fin portion 15 and the bottom portion 18 cof the gate electrode groove 18. In the ion implantation, after thefirst ion implantation is performed under conditions in which energy is15 KeV and a dose amount is 5E14 atoms/cm², the second ion implantationis performed under conditions in which energy is 30 KeV and a doseamount is 2E13 atoms/cm² (implantation in two steps).

Thereby, the second impurity diffusion region 29 is formed to cover allof the portions other than the lower end of the gate insulating film 21provided on the second side 18 b of each of the two gate electrodegrooves 18 and the first and second transistors 19-1 and 19-2 thatinclude the gate insulating film 21, the fin portion 15, the gateelectrode 22, the buried insulating film 24, the first impuritydiffusion region 28, and the second impurity diffusion region 29 areformed.

As such, the fin portion 15 is provided in the bottom portion 18 c ofthe gate electrode groove 18 and the first impurity diffusion region 28that includes the top surface 13 a of the semiconductor substrate 13interposed between the first side 18 a and the second element isolationgroove 54 and covers the upper portion 21A of the gate insulating film21 arranged on the first side 18 a and the second impurity diffusionregion 29 that is arranged on the portion of the semiconductor substrate13 positioned between the two gate electrode grooves 18 and covers allof the portions other than the lower end of the gate insulating film 21arranged on the second side 18 b of each of the pair of gate electrodegrooves 18 are provided. Thereby, when the first and second transistors19-1 and 19-2 are operated, the first channel region is formed in thefin portion 15, the second channel region is formed in the portions ofthe semiconductor substrate 13 that contacts the lower portion of thegate insulating film 21 arranged on the first side 18 a, contacts thebottom portion 18 c of the gate electrode groove 18, and is positionedat the lower side of the bottom portion of the second impurity diffusionregion 29 arranged on the second side 18 b, and the channel region isnot provided in the portion of the semiconductor substrate 13 thatcontacts the second side 18 b and is positioned at the upper side of thebottom portion of the second impurity diffusion region 29.

In other words, when the first and second transistors 19-1 and 19-2 areturned on, the fin portion 15 is fully depleted. Therefore, in the firstand second transistors 19-1 and 19-2, the resistance becomes low and thecurrent can easily flow, as compared with the transistors according tothe related art. Thereby, in a miniaturized memory cell, the channelresistance may be decreased and the on-state current may be increased.

When one of the first and second transistors 19-1 and 19-2 is operated,the other transistor may be suppressed from being erroneously operated.

Therefore, even when the size of the semiconductor device 10 isdecreased and the gate electrodes 22 are arranged at a narrow pitch, thefirst and second transistors 19-1 and 19-2 may be operated independentlyand stably.

The fin portion 15 is provided in the bottom portion 18 c of each of thetwo gate electrode grooves 18 arranged to be adjacent to each other andthe depth H of the fin portion 15 is set to 40 nm or less. Thus, in thestate in which “L” is stored in the lower electrode 57 electricallyconnected to the first transistor 19-1 and “H” is stored in the lowerelectrode 57 electrically connected to the second transistor 19-2, whenon/off of the gate electrode 22 (word line) corresponding to the firsttransistor 19-1 is repeated, the fin portion 15 becoming the channelregion of the first transistor 19-1 is a p-type and it becomes difficultto induce the electrons e⁻ (not shown in the drawings). For this reason,the electrons e⁻ induced in the channel of the first transistor 19-1 maybe suppressed from reaching the second impurity diffusion region 28(drain region) forming the second transistor 19-2.

Thereby, the electrons e⁻ induced in the channel of the first transistor19-1 may be prevented from destroying H information stored in the lowerelectrode 57 electrically connected to the second transistor 19-2 tochange the state to the L state. Therefore, generation of thedisturbance failure in which the operation state of one adjacent cellchanges a storage state of the other cell may be suppressed.

In the DRAM in which the interval between the two gate electrodes 22arranged to be adjacent to each other is 50 nm or less, the generationof the disturbance failure may be suppressed.

Next, in the processes shown in FIGS. 13A to 13C, the photoresist 73shown in FIGS. 12A to 12C is removed.

Next, in the processes shown in FIGS. 14A and 14B, the bit line contactplug 33 that buries the opening 32 and the bit line 34 (refer to FIG. 1)that is arranged on the bit line contact plug 33 and extends in the Xdirection are collectively formed.

Specifically, as shown in FIG. 14A, the polysilicon film, the titaniumnitride film, and the tungsten film (not shown in the drawings) aresequentially formed (at this time, formed such that the polysilicon filmburies the opening 32) on the top surface 24 a of the buried insulatingfilm 24 to bury the opening 32.

Next, a silicon nitride film (SiN film) (not shown in the drawings) thatbecomes a base material of the cap insulating film 36 is formed on thetungsten film (not shown in the drawings).

Next, a photoresist (not shown in the drawings) that covers a formationregion of the bit line 34 is formed on the silicon nitride film (SiNfilm) using a photolithographic technique.

Next, the silicon nitride film (SiN film), the tungsten film, thetitanium nitride film, and the polysilicon film are patterned byanisotropic etching (specifically, dry etching) using the photoresist asa mask, and the cap insulating film 36 that is formed of the siliconnitride film (SiN film), the bit line contact plug 33 that is formed ofthe polysilicon film and contacts the top surface 29 a of the secondimpurity diffusion region 29, and the bit line 34 that is arranged onthe bit line contact plug 33 and includes the polysilicon film, thetitanium nitride film, and the tungsten film are collectively formed.

Next, the silicon nitride film (SiN film) and the silicon oxide film(SiO₂ film) (not shown in the drawings) are sequentially formed to coverthe side of the bit line 34 and the cap insulating film 36. Next, thesidewall film 37 that covers the side of the cap insulating film 36 andthe side of the bit line 34 is formed by etching the entire surfaces ofthe silicon oxide film (SiO₂ film) and the silicon nitride film (SiNfilm).

As such, when the sidewall film 37 is formed by sequentially stackingthe silicon nitride film (SiN film) and the silicon oxide film (SiO₂film) and the coating-based insulating film (specifically, silicon oxidefilm (SiO₂ film)) formed by an SOG method is formed as the interlayerinsulating film 38, wettability of the silicon oxide film (coating-basedinsulating film) is improved. Therefore, a void may be suppressed frombeing generated in the silicon oxide film (coating-based insulatingfilm).

Next, the interlayer insulating film 38 that covers the sidewall film 37and has the top surface 38 a flush with the top surface 36 a of the capinsulating film 36 is formed on the top surface 24 a of the buriedinsulating film 24, the top surface 26 a of the mask insulating film 26,and the top surface 55 a of the second element isolation insulating film55. Thereby, the top surface 36 a of the cap insulating film 36 isexposed from the interlayer insulating film 38.

Specifically, the coating-based insulating film (silicon oxide film(SiO₂ film)) that is formed by an SOG method is coated on the topsurface 24 a of the buried insulating film 24, the top surface 26 a ofthe mask insulating film 26, and the top surface 55 a of the secondelement isolation insulating film 55 to cover the sidewall film 37.Next, the silicon oxide film (coating-based insulating film) may bedensified by performing the heat treatment.

When the silicon oxide film (coating-based insulating film) is formed bythe SOG method, a coating liquid that contains polysilazane is used. Theheat treatment may be performed under a water-vapor atmosphere.

Next, the silicon oxide film (coating-based insulating film) on whichthe heat treatment is performed is polished by a CMP method, until thetop surface 36 a of the cap insulating film 36 is exposed. Thereby, theinterlayer insulating film 38 that has the top surface 38 a flush withthe top surface 36 a of the cap insulating film 36 is formed.

In the structure shown in FIGS. 14A and 14B, although not shown in thedrawings, the silicon oxide film (SiO₂ film) that covers the top surface36 a of the cap insulating film 36 and the top surface 38 a of theinterlayer insulating film 38 may be formed by a CVD method, after thesilicon oxide film (coating-based insulating film) is polished.

Next, in the processes shown in FIGS. 15A and 15B, by a self alignedcontact (SAC) method, the interlayer insulating film 38, the maskinsulating film 26, the buried insulating film 24, and the gateinsulating film 21 are etched by anisotropic etching (specifically, dryetching) and the contact hole 41 that exposes a part of the top surface28 a of the first impurity diffusion region 28 is formed.

At this time, the dry etching is divided into a step of selectivelyetching the silicon oxide film (SiO₂ film) and a step of selectivelyetching the silicon nitride film (SiN film) and is performed.

Next, the capacitor contact plug 42 of which the top surface 42 a isflush with the top surface 38 a of the interlayer insulating film 38 andthe lower end contacts the top surface 28 a of the first impuritydiffusion region 28 is formed in the contact hole 41.

Specifically, the titanium nitride film (not shown in the drawings) andthe tungsten film (not shown in the drawings) are sequentially stackedby a CVD method to bury the contact hole 41. Next, the unnecessarytitanium nitride film and tungsten film that are formed on the topsurface 38 a of the interlayer insulating film 38 are removed bypolishing by a CMP method and the capacitor contact plug 42 thatincludes the titanium nitride film and the tungsten film is formed inthe contact hole 41.

Next, the capacitor contact pad 44 that contacts a part of the topsurface 42 a of the capacitor contact plug 42 is formed on the topsurface 38 a of the interlayer insulating film 38.

Specifically, a metallic film (not shown in the drawings) that becomes abase material of the capacitor contact pad 44 is formed to cover the topsurface 36 a of the cap insulating film 36, the top surface 42 a of thecapacitor contact plug 42, and the top surface 38 a of the interlayerinsulating film 38.

Next, the photoresist (not shown in the drawings) that covers a surfacecorresponding to a formation region of the capacitor contact pad 44 inthe top surface of the metallic film is formed on the silicon nitridefilm (SiN film) using a photolithographic technique. Next, theunnecessary metallic film that is exposed from the photoresist isremoved by dry etching using the photoresist as a mask and the capacitorcontact pad 44 that is formed of the metallic film is formed. After thecapacitor contact pad 44 is formed, the photoresist (not shown in thedrawings) is removed.

Next, the silicon nitride film 46 that covers the capacitor contact pad44 is formed on the top surface 36 a of the cap insulating film 36, thetop surface 42 a of the capacitor contact plug 42, and the top surface38 a of the interlayer insulating film 38.

Next, in the processes shown in FIGS. 16A and 16B, the thick siliconoxide film (SiO₂ film) (not shown in the drawings) is formed on thesilicon nitride film 46. The thickness of the silicon oxide film (SiO₂film) may be set to 1500 nm.

Next, the patterned photoresist (not shown in the drawings) is formed onthe silicon oxide film (SiO₂ film) using a photolithographic technique.Next, the silicon oxide film (not shown in the drawings) and the siliconnitride film 46 that are formed on the capacitor contact pad 44 areetched by dry etching using the photoresist as a mask and a cylinderhole (not shown in the drawings) that exposes the capacitor contact pad44 is formed. Next, the photoresist (not shown in the drawings) isremoved.

Next, a conductive film (for example, titanium nitride film) is formedon an inner surface of the cylinder hole (not shown in the drawings) andthe top surface of the capacitor contact pad 44 and the lower electrode57 that is formed of the conductive film and has a coronal shape isformed.

Next, the silicon oxide film (not shown in the drawings) is removed bywet etching and the top surface of the silicon nitride film 46 isexposed. Next, the capacitor insulating film 58 that covers the topsurface of the silicon nitride film 46 and the lower electrode 57 isformed.

Next, the upper electrode 59 is formed to cover the surface of thecapacitor insulating film 58. At this time, the upper electrode 59 isformed such that the top surface 59 a of the upper electrode 59 isarranged on the upper side of the capacitor insulating film 58. Thereby,the capacitor 48 that includes the lower electrode 57, the capacitorinsulating film 58, and the upper electrode 59 is formed on eachcapacitor contact pad 44.

Thereby, the semiconductor device 10 according to the first embodimentis manufactured. Actually, an interlayer insulating film, a via, and awiring (not shown in the drawings) are formed on the top surface 59 a ofthe upper electrode 59.

According to the method of manufacturing the semiconductor deviceaccording to the first embodiment, the fin portion 15 is provided in thebottom portion 18 c of the gate electrode groove 18. The first impuritydiffusion region 28 that includes the top surface 13 a of thesemiconductor substrate 13 interposed between the first side 18 a andthe second element isolation groove 54 and covers the upper portion 21Aof the gate insulating film 21 arranged on the first side 18 a, and thesecond impurity diffusion region 29 that is arranged on the portion ofthe semiconductor substrate 13 positioned between the two gate electrodegrooves 18 and covers all of the portions other than the lower end ofthe gate insulating film 21 arranged on the second side 18 b of each ofthe pair of gate electrode grooves 18 are provided. Thereby, when thefirst and second transistors 19-1 and 19-2 are operated, the firstchannel region is formed in the fin portion 15, the second channelregion is formed in the portion of the semiconductor substrate 13 thatcontacts the lower portion of the gate insulating film 21 arranged onthe first side 18 a, contacts the bottom portion 18 c of the gateelectrode groove 18, and is positioned at the lower side of the bottomportion of the second impurity diffusion region 29 arranged on thesecond side 18 b, and the channel region may not be provided in theportion of the semiconductor substrate 13 that contacts the second side18 b and is positioned at the upper side of the bottom portion of thesecond impurity diffusion region 29.

That is, when the first and second transistors 19-1 and 19-2 are turnedon, the fin portion 15 is fully depleted. Therefore, in the first andsecond transistors 19-1 and 19-2, the resistance becomes low and thecurrent can easily flow, as compared with the transistors according tothe related art. Thereby, in a miniaturized memory cell, the channelresistance may be decreased and the on-state current may be increased.

When one of the first and second transistors 19-1 and 19-2 is operated,the other transistor may be suppressed from being erroneously operated.

Therefore, even when the size of the semiconductor device 10 isdecreased and the gate electrodes 22 are arranged at a narrow pitch, thefirst and second transistors 19-1 and 19-2 may be operated independentlyand stably.

The fin portion 15 is provided in the bottom portion 18 c of each of thetwo gate electrode grooves 18 arranged to be adjacent to each other andthe depth H of the fin portion 15 is set to 40 nm or less. Thus, in thestate in which “L” is stored in the lower electrode 57 electricallyconnected to the first transistor 19-1 and “H” is stored in the lowerelectrode 57 electrically connected to the second transistor 19-2, whenon/off of the gate electrode 22 (word line) corresponding to the firsttransistor 19-1 is repeated, the fin portion 15 becoming the channelregion of the first transistor 19-1 is a p-type and it becomes difficultto induce the electrons e⁻ (not shown in the drawings). Therefore, theelectrons e⁻ induced in the channel of the first transistor 19-1 may besuppressed from reaching the second impurity diffusion region 28 (drainregion) forming the second transistor 19-2.

Thereby, the electrons e⁻ induced in the channel of the first transistor19-1 may be prevented from destroying H information stored in the lowerelectrode 57 electrically connected to the second transistor 19-2 tochange the state to the L state. Therefore, generation of thedisturbance failure in which the operation state of one adjacent cellchanges a storage state of the other cell may be suppressed.

In the DRAM in which an interval between the two gate electrodes 22arranged to be adjacent to each other is 50 nm or less, the generationof the disturbance failure may be suppressed.

The gate electrode 22 is formed to bury the lower portion of each gateelectrode groove 18 through the gate insulating film 21. Next, theburied insulating film 24 that covers the top surface 22 a of the gateelectrode 22 is formed to bury each gate electrode groove 18 and thegate electrode 22 may be prevented from protruding to the upper side ofthe surface 13 a of the semiconductor substrate 13.

Thereby, as described in this embodiment, when the DRAM is used as thesemiconductor device 10, the bit line 34 or the capacitor 48 that isformed in the process after the process for forming the gate electrode22 may be easily formed. Therefore, the semiconductor device 10 may beeasily manufactured.

In this embodiment, the silicon oxide film (SiO₂ film) is used as theburied insulating film 24 and the silicon nitride film (SiN film) isused as the mask insulating film 26. However, the silicon nitride film(SiN film) may be used as the buried insulating film 24 and the siliconoxide film (SiO₂ film) may be used as the mask insulating film 26.

Thereby, in the processes shown in FIGS. 15A and 15B, when the contacthole 41 is formed, the silicon nitride film (SiN film) that becomes theburied insulating film 24 functions as an etching stopper. Therefore,because the contact hole 41 may be prevented from exposing the topsurface 22 a of the gate electrode 22, the capacitor contact pad 44 andthe gate electrode 22 may be prevented from becoming conductive, throughthe capacitor contact plug 42 formed in the contact hole 41.

The preferred embodiments of the present invention have been describedin detail. However, the present invention is not limited to the specificembodiments and various changes and modifications may be made withoutdeparting from the spirit and scope of the present invention describedin claims.

FIG. 17 is a plan view showing another example of the layout of a memorycell array that may be applied to the semiconductor device according tothe embodiment of the present invention. In FIG. 17, the same componentsas those of the structure shown in FIG. 1 are denoted by the samereference numerals.

The semiconductor device 10 according to the embodiment described abovecan also be applied to the layout in which the active region 16 and thebit line 34 shown in FIG. 17 are formed in a zigzag shape.

As used herein, the following directional terms “forward, rearward,above, downward, vertical, horizontal, below, and transverse” as well asany other similar directional terms refer to those directions of anapparatus equipped with the present invention. Accordingly, these terms,as utilized to describe the present invention should be interpretedrelative to an apparatus equipped with the present invention.

The term “configured” is used to describe a component, section or partof a device includes hardware and/or software that is constructed and/orprogrammed to carry out the desired function.

Furthermore, the particular features, structures, or characteristics maybe combined in any suitable manner in one or more embodiments.

The terms of degree such as “substantially,” “about,” and“approximately” as used herein mean a reasonable amount of deviation ofthe modified term such that the end result is not significantly changed.For example, these terms can be construed as including a deviation of atleast ±5 percents of the modified term if this deviation would notnegate the meaning of the word it modifies.

It is apparent that the present invention is not limited to the aboveembodiments, but may be modified and changed without departing from thescope and spirit of the invention.

1. A semiconductor device comprising: a semiconductor substrate having afirst gate groove; a first fin structure underneath a top of the firstgate groove; a second gate groove in the semiconductor substrate runninggenerally parallel to said first gate groove; a second fin structureunderneath a top of the second gate groove; a first gate insulating filmthat covers the first gate groove and a surface of the first finstructure; a second gate insulating film that covers the second gategroove and a surface of the second fin structure; a first gate electrodeon the first gate insulating film in a lower portion of the first gategroove, the first gate electrode extending over the first fin structure;a second gate electrode on the second gate insulating film in a lowerportion of the second gate groove, the second gate electrode extendingover the second fin structure; a first diffusion region in thesemiconductor substrate, the first diffusion region covering an upperportion of a first side of the first gate groove; a second diffusionregion in the semiconductor substrate, the second diffusion regioncovering a second side of the first gate groove, the second diffusionregion also covering a second side of the second gate groove; a thirddiffusion region in the semiconductor substrate covering an upperportion of a first side of the second gate groove, wherein the firstgate electrode and the second gate electrode are separated by a distanceof less than 50 nm.
 2. The semiconductor device according to claim 1,wherein a bottom of the second diffusion region is shallower than abottom of the first fin structure.
 3. The semiconductor device accordingto claim 1, wherein the first gate groove has a bottom that has a depthfrom a surface of the semiconductor substrate in the range from 150 nmto 200 nm, and the first fin structure has a height in the range from 10nm to 40 nm. 4.-20. (canceled)
 21. The semiconductor device according toclaim 1, further comprising a plurality of first isolation regions inthe semiconductor device, the plurality of first isolation regionsdefining active regions, the plurality of first isolation regionsextending in a first direction, wherein the first and second gategrooves extend in a second direction and across the active regions andthe plurality of first isolation regions.
 22. A semiconductor devicecomprising: a semiconductor substrate having a first gate groove; afirst fin structure underneath top of the first gate groove; a firstdiffusion region in the semiconductor substrate, the first diffusionregion covering an upper portion of a first side of the first gategroove; and a second diffusion region in the semiconductor substrate,the second diffusion region covering a second side of the first gategroove.